Device for adjusting light intensity for discharge lamp projectors

ABSTRACT

The invention relates to a device for adjusting light intensity for discharge lamp projectors comprising an optical assembly ( 1 ) comprised of a discharge lamp ( 3 ) and a spherical mirror ( 2 ), and of a Fresnel lens ( 4 ), provided in front of the lamp ( 3 ) of said optical assembly ( 1 ), characterised in that an iris diaphragm ( 5 ) is provided on said optical assembly ( 1 ), in front of the lamp ( 3 ), in correspondence of the focus of the optical assembly ( 1 ).

The present invention relates to a device for adjusting light intensity for discharge lamp projectors.

More specifically, the invention relates to a device of the above kind allowing to obtain an adjustment of intensity avoiding all the drawbacks of the known systems.

As it is well known, operation of discharge lamps is based on a voltaic arc determined by the discharge between two electrodes. It is also known that it is not possible to obtain in this kind of lamps an adjustment of intensity in the range between 0% and 100%, as it is possible for filament lamps, since it would cause the switching off of the arc and in any case a very unstable operation at the intermediate power values.

At present, to obtain the adjustment of the light intensity of the discharge lamp, a mechanical shutter is mounted in front of the projector, making it possible to vary the light intensity, blocking the light rays emitted from the projector.

This kind of solution, even if used since many years, is characterised by some drawbacks, among which it is possible to mention a remarkable increase of weight, sizes and unbalancing of the weight with respect to the fulcrum of the projector, as well as a remarkable increase of total costs.

Mainly, said solution induces geometric aberrations of the emitted light beam, reducing the light efficiency of the projector when the shutter is fully open.

In view of the above, it is well evident the advantage of having at disposal a device as the one suggested according to the present invention, allowing to solve all the above mentioned problems.

It is therefore specific object of the present invention a device for adjusting light intensity for discharge lamp projectors comprising an optical assembly comprised of a discharge lamp and a spherical mirror, and of a Fresnel lens, provided in front of the lamp of said optical assembly, characterised in that an iris diaphragm is provided on said optical assembly, in front of the lamp, in correspondence of the focus of the optical assembly.

Preferably, according to the invention, said optical assembly is movable along a longitudinal axis between two different foci, respectively a “flood” or “large beam” point and a “spot” or “narrow beam” point.

The present invention will be now described, for illustrative but not limitative purposes, according to its preferred embodiment, with particular reference to the FIGURE of the enclosed drawing showing a schematic view of an embodiment

Observing now the FIGURE of the enclosed drawing, it is shown a device according to the invention, providing an assembly 1, comprising a spherical mirror 2 and a lamp 3, said assembly being movable according to arrows A shown in the FIGURE.

In front of the movable assembly 1 it is provided a Fresnel lens 4, that must create the light beam.

According to the invention, an iris diaphragm 5 is provided on said optical assembly, in correspondence of the focus of the lamp 3.

The use of an iris diaphragm 5 provided close to the lamp 3 within a Fresnel 4 lens projector, interposed between the optical assembly 1 inside the projector and the lens 4, and integral with the movable element, is the most characterising feature according to the invention.

As it is well known, in a Fresnel lens, the assembly 1 must be moved between two foci, to allow the variation of the opening of the light beam emitted from the projector (FLOOD=large beam=optical assembly 1 placed close to the lens 4; SPOT=narrow beam optical beam 1 placed on the focus farther from the lens 4).

During this run, serving to focus the beam, the incidence angle of the concentric light rays emitted from the inner optical assembly 1 (lamp 3-mirror 2) on the lens varies.

By using an iris diaphragm 5 provided close to the light source 3, moving integrally with the latter source along the optical axis, it is reproduced the focus of the optical assembly at the centre of the iris, allowing a modulation of the light amount without altering the geometry and the direction of the (concentric) light rays, but only blocking the amount of the same.

Summarising, the device according to the invention allows to adjust light intensity (dimmer effect) acting on the light rays emitted from the inner optical assembly 1, without modifying the direction and without creating any shadow, since it acts on the beam before the Fresnel lens 4.

By the device according to the invention, it is realised a kind of (integrated) mechanical optical-dimmer within the projector, so that a weight, cost and size reduction is obtained with respect to the known solutions providing mechanical dimmers mounted in front of the projectors.

Furthermore, by the solution according to the invention, photometric features, uniformity of emitted light and light efficiency of the projector are obtained without the influence of the presence of the inventive device, since iris is fully open the spot and flood values of light intensity, amplitude and uniformity of the light beam correspond to those of the same standard projector without mechanical dimmer, this result not being obtained by the conventional mechanical dimmers, since they are mounted after the Fresnel lens introducing optical aberrations (not uniform light beam) and often, according to the various specific cases, influence the light emission reducing its intensity, also when they are completely open (for example horizontal or vertical blade shutters).

Furthermore, thanks to the intrinsic design economy of the system with respect to what is available today on the market, the solution according to the invention, if used on small size projectors mounting the various kinds of low electric power and high luminous efficiency discharge lamps available on the market, allows to expand the use of an energy saving technology to different professional fields (video production, movies, events, fashion, shows, theatre and architecture).

The present invention has been described for illustrative but not limitative purposes, according to its preferred embodiments, but it is to be understood that modifications and/or changes can be introduced by those skilled in the art without departing from the relevant scope as defined in the enclosed claims. 

1. Device for adjusting light intensity for discharge lamp projectors comprising an optical assembly comprised of a discharge lamp and a spherical mirror, and of a Fresnel lens, provided in front of the lamp of said optical assembly, characterised in that an iris diaphragm is provided on said optical assembly, in front of the lamp, in correspondence of the focus of the optical assembly.
 2. Device for adjusting light intensity for discharge lamp projectors according to claim 1, characterised in that said optical assembly is movable along a longitudinal axis between two different foci, respectively a “flood” or “large beam” point and a “spot” or “narrow beam” point.
 3. Device for adjusting light intensity for discharge lamp projectors according to claim 1, substantially as illustrated and described.
 4. Device for adjusting light intensity for discharge lamp projectors according to claim 2, substantially as illustrated and described. 